VUV PHOTON SOURCE OF A MICROWAVE EXCITED MICROPLASMAS AT LOW PRESSURE* Peng Tian a) , Mark Denning b) and Mark J. Kushner a) a) University of Michigan, Ann Arbor, MI 48109 USA [email protected], [email protected]) Agilent Technologies, 5301 Stevens Creek Blvd, Santa Clara, CA [email protected]* Work supported by Agilent Technologies.
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VUV PHOTON SOURCE OF A MICROWAVE EXCITED MICROPLASMAS AT LOW PRESSURE* Peng Tian a), Mark Denning b) and Mark J. Kushner a) a) University of Michigan,
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VUV PHOTON SOURCE OF A MICROWAVE EXCITED MICROPLASMAS AT LOW PRESSURE*
b)Agilent Technologies, 5301 Stevens Creek Blvd, Santa Clara, [email protected]
* Work supported by Agilent Technologies.
· Microplasma UV/VUV photon sources
· Split Ring Microwave Micro-plasma
· Description of model
· Photon generation
· Pressure
· Pd Scaling
· Pulsing with Ar/He gas mixtures
· Concluding Remarks
AGENDA
University of MichiganInstitute for Plasma Science & Engr.MIPSE_2013 P.T.
University of MichiganInstitute for Plasma Science & Engr.
· Rare gas microplasmas are efficient and discretely tunable UV/VUV light sources.
· Compact, inexpensive microplasma light sources have many applications ranging from analytical chemistry, mass spectrometry and surface analysis.
· Controlling metastable fluxes, light wavelengths and ion, VUV photon fluxes are important to achieving chemical selectivity.
· Microwave excited microplasmas can provide lower excitation voltage, high power efficiency and longer life time of the devices compared with DC microplasmas.
· In this project, a microwave excited microplasma light source by a split-ring resonator (SRR) antenna will be studied as discretely tunable VUV source.
MIPSE_2013 P.T.
UV/VUV PHOTON SOURCES BY MICROPLASMA
· A microstrip split-ring resonator was investigated to ignite and sustain a RF microplasma proposed by N. Miura and J. Hopwood.
· This concept was further developed as a SRR microplasma cavity as VUV light source.
SPLIT-RING-RESONATOR (SRR) MICROPLASMA CAVITY
University of MichiganInstitute for Plasma Science & Engr.MIPSE_2013 P.T.
SRR-GEOMETRY BASE CASE
University of MichiganInstitute for Plasma Science & Engr.
· Microwave capacitively coupled plasma excited by push-pull electrodes.
University of MichiganInstitute for Plasma Science & Engr.MIPSE_2013 P.T.
· As pressure increases (cavity size decreases):
· The photon source is more focused at center of the cavity, providing larger viewing angle to top plane.
· Power efficiency of photon source increases.
· Photon Flux vs. Power
Photon Flux
University of MichiganInstitute for Plasma Science & Engr.
· Electron temperature over-shoots at the beginning of pulse.
· Bulk averaged photon flux and ion density peaked during pulse-on time.
· 200 kHz PRF, 10% DC, 160 V.
MIPSE_2013 P.T.
· Bulk Ion Density and Photon Flux
· Te and Plasma Potential
PULSING - GAS MIXTURES: Ar
University of MichiganInstitute for Plasma Science & Engr.
· With more He, larger over-shoot of Te enhanced photon generation during pulse-on period.
MIPSE_2013 P.T.
PULSING - GAS MIXTURES: He/ArHe/Ar=90/10He/Ar=70/30He/Ar=10/90
University of MichiganInstitute for Plasma Science & Engr.
· Pening ionization is depleting He radiative states during afterglow.
· Ar+ is always the dominant ion in plasma. MIPSE_2013 P.T.
PULSING - GAS MIXTURES: He/ArHe/Ar=90/10He/Ar=70/30He/Ar=10/90
CONCLUDING REMARKS
University of MichiganInstitute for Plasma Science & Engr.MIPSE_2013 P.T.
· Modeling of a microwave excited SRR microplasmas as sources of VUV light.
· Pure Ar plasma at 4 Torr, 2 W produces peak electron density close to 1014 cm-3, a fractional ionization of 1%.
· Shape and position of light source in plasma can be controlled by pressure.
· The relative size of light source in plasma and power efficiency of photon flux generation is related to the size of the cavity, with p*d scale kept unchanged.
· Pulsing with He addition could increase Te and thus enhanced pulsing effect.
BACKUP SLIDES
· Microplasmas as VUV light source for resonance absorption spectroscopy
University of MichiganInstitute for Plasma Science & Engr.MIPSE_2013 P.T.
APPLICATION OF MICROWAVE LIGHT SOURCES
· Electron Energy Distributions – Electron Monte Carlo Simulation
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· Phase dependent electrostatic fields· Phase dependent electromagnetic fields· Electron-electron collisions using particle-mesh algorithm· Phase resolved electron currents computed for wave equation
solution.· Captures long-mean-free path and anomalous behavior.· Separate calculations for bulk and beam (secondary electrons)
HPEM-EQUATIONS SOLVED - ,, rf
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HPEM-EQUATIONS SOLVED - ,rN
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VARYING PRESSURE AND POWER: CONDITION
· Based on base case condition, change pressure and power.
· Power deposited per particle is kept constant by keeping Power/Pressure = 0.5 W/Torr
Pressure (Torr) Power (W)
4 2
6 3
8 4
10 5
12 6
16 8
20 10
MIPSE_2013 P.T.
PULSED PLASMAS
University of MichiganInstitute for Plasma Science & Engr.
· Carrier frequency is modulated by a pulse, a fixed pulsing voltage and duty cycle.
· The fast rising edge can “over-shoot” the self sustaining E/N, raising the “hot tail” in EEDF f().